Field of Invention
Various embodiments relate to an electronic device, and more particularly, to a voltage generator, a semiconductor memory device having the same, and a method of operating the semiconductor memory device.
Description of Related Art
Semiconductor memory devices are typically categorized into volatile memory devices and non-volatile memory devices.
Volatile memory devices perform write and read operations at high speed, but they are unable to retain data stored therein without a constant source of power. Non-volatile memory devices perform write and read operations at relatively low speed, but they may retain their stored data regardless of whether they have a constant source of power. The non-volatile memory devices include Read Only Memory (ROM), Mask ROM (MROM), Programmable ROM (PROM), Erasable Programmable ROM (EPROM), Electrically Erasable and Programmable ROM (EEPROM), flash memory, Phase-change Random Access Memory (PRAM), Magnetic RAM (MRAM), Resistive RAM (RRAM) and Ferroelectric RAM (FRAM). Flash memories may be NOR type or NAND type.
Flash memories have the advantages of both RAM and ROM. That is, flash memories may be freely programmed and erased similar to RAM. Similar to ROM, flash memories may retain stored data even without power. Flash memories have been widely used as the storage media of portable electronic devices such as mobile phones, digital cameras, personal digital assistants (PDAs), and MP3 players.
In semiconductor memory devices, to prevent a latch-up and unstable variations of threshold voltages of MOS transistors caused by the body effect, bulk voltages are to be applied to bulks of PMOS transistors and NMOS transistors within a semiconductor memory device.
Bulk voltages applied to the PMOS transistors and the NMOS transistors can the amount leakage current of PMOS and NMOS transistors that are in the off state, as well as the operating speed of the transistors. In other words, the amount of leakage current and the operating speed of the NMOS transistors may decrease when the bulk voltage is lower than its source terminal voltage. In addition, the amount of leakage current and the operating speed of the PMOS transistors may decrease with bulk voltages that are higher than the voltage of its source terminal.